Denver Air Quality in Summer
Across 2019–2025, Denver's summer (June–August) air quality had a median AQI of 84 (Moderate) over 644 monitored days in the Denver-Aurora-Lakewood, CO area. 30.9% of summer days (199 of 644) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 94.6% of days. The cleanest summer on record here was 2025 (median AQI 71, 11 days above 100) and the worst was 2021 (median 112, 56 days above 100, peak AQI 177).
- Good: 5.1%
- Moderate: 64.0%
- Unhealthy for Sensitive Groups: 26.6%
- Unhealthy or worse: 4.3%
Reduce Indoor Ozone in Denver
Today's main pollutant in Denver is ground-level ozone (AQI 43). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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How is the air in Denver in summer?
Moderate on a typical day: median AQI 84 across 2019–2025, with 30.9% of summer days above AQI 100. Ground-level ozone is the main driver.
- ✓5.1% of summer days were Good (AQI 0–50), 64.0% Moderate (51–100).
- ✓199 days of 644 reached AQI 101+; the summer peak was 177.
- ✓Cleanest month: June; worst month: July.
Frequently asked questions
What is the air quality like in Denver in summer?▾
Across 2019–2025, the median daily AQI in Denver in summer was 84 (Moderate). 5.1% of days were Good, 64.0% Moderate, and 30.9% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in Denver?▾
A typical summer day in Denver is Moderate (median AQI 84): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 3 of summer days (30.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Denver's summer air quality problems?▾
Ground-level ozone set the daily AQI on 94.6% of summer days in Denver. The highest summer AQI recorded in 2019–2025 was 177 (Unhealthy), in 2021.
Denver summer air quality, year by year
Denver summer air quality by year (Denver-Aurora-Lakewood, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 92 | 80 | 20 | 154 | O3 |
| 2020 | 92 | 80 | 25 | 161 | O3 |
| 2021worst | 92 | 112 | 56 | 177 | O3 |
| 2022 | 92 | 92 | 31 | 169 | O3 |
| 2023 | 92 | 84 | 21 | 143 | O3 |
| 2024 | 92 | 90 | 35 | 174 | O3 |
| 2025cleanest | 92 | 71 | 11 | 122 | O3 |
What summer air means in Denver
A typical summer day in Denver is Moderate (median AQI 84): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 3 of summer days (30.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Summer's median AQI of 84 is above Denver's whole-year median of 64, making it one of the area's dirtier periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so Denver runs above the national Summer norm; 30.9% of its Summer days topped AQI 100 versus 3.6% nationally (above average).
Within the season, June is the cleanest month (median AQI 77, 20.0% of days above 100) and July the worst (median 90, 38.7% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Denver
The latest EPA AirNow observation puts Denver's AQI at 43 (O3). The figures above are multi-year season statistics, not today's reading.
View current Denver air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Denver-Aurora-Lakewood, CO), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.